To maintain the competitive edge of the 3rd Generation Partnership Project (3GPP) system in the next 10 years or a longer period, the 3GPP organization is making a research on access technology evolution. Particularly, to improve the capability of the 3GPP system to process fast growing IP data traffic, the packet technology used in the 3GPP system must be enhanced. The most important parts in the technology evolution include delay reduction, higher user data rate, enhanced system capacity and wider coverage, and reduction of an operator's total costs. In addition, the compatibility of the evolved network structure with the existing network is also an important index. To protect the existing investments of the operators and fully use traditional entities in a circuit switched (CS) domain, the prior art provides a solution for carrying CS data and signaling in a packet switched (PS) domain in an evolved network. This solution is called an evolved mobile switching centre (eMSC) solution. The eMSC solution in the existing standard is described herein. In a long term evolution (LTE)/system architecture evolution (SAE) network, the CS domain controls voice services of calls on a centralized basis. This solution uses a same control entity, for example, the eMSC, to control services from different access areas and simplifies the voice service continuity between the CS domain and the LTE/SAE network. In the eMSC solution, a UE can simultaneously connect to the IP multimedia sub-system (IMS) and the MSC to process different services. In addition, the eMSC solution provides a new network entity—eMSC, proposes new interfaces and gives some theoretical suggestions.
FIG. 1 is a block diagram of the eMSC solution in the prior art. Only a signaling path is given in FIG. 1. As shown in FIG. 1, the evolved radio network includes an evolved NodeB (eNB), an access gateway (AGW) module, and an eMSC. The AGW module includes a former mobility management module and a former user plane management module and acts as the user plane anchor between different access systems. The eMSC is a new entity for controlling CS voice services with most functions similar to those of a former MSC. For example, the eMSC has CS-oriented C and D interfaces and a PS-oriented Rx interface on the control plane that establishes a PS domain bearer through a policy and charging control (PCC) system.
However, the solution in the prior art does not describe how the UE is handed over between a PS network and a CS network by using the eMSC. That is, the solution in the prior art does not describe how the UE is handed over from a PS network to a CS network and from a CS network to a PS network by using the eMSC.
In addition, the solution in the prior art does not describe how the UE is reattached to a target eMSC when an eMSC to which the UE is attached is changed.